When etching and film formation are performed on a semiconductor wafer, normally single semiconductor-wafer production equipment, with excellent reaction control, is used. The semiconductor wafer is placed on the surface of a holder which is positioned within a reaction chamber, and may be left as is, or may be fixed in place mechanically, or may be chucked in place by electrostatic force by applying a voltage to an electrode embedded in the holder, or otherwise fixed to the holder.
The temperature of the semiconductor wafer held in this way is rigorously controlled, in order to maintain uniformity of the film formation rate and etch rate during CVD (chemical vapor deposition), plasma CVD or similar, or during etching, plasma etching or similar. In order to perform such rigorous temperature control, the holder is heated by a heating element incorporated in the holder, so that the semiconductor wafer is heated by heat transmitted from the surface thereof.
A holder having a heating element embedded therein is formed by, for example, embedding an Mo coil in a ceramic material. W or Mo electrodes connected to an Mo coil are provided on the opposite face (rear face) from the surface of the holder which holds the material to be treated; Ni or other lead wires are joined to the electrode ends and connected to an external power supply, so that heating is performed by supplying power to the Mo coil embedded in the ceramic holder.
Within the above reaction chamber, often a halogen gas or other corrosive gas is used as the reaction gas, and so the W or Mo electrodes exposed on the rear surface of the holder tend to be corroded. Hence by hermetically sealing a ceramic or metal cylindrical support member with excellent corrosion resistance to the rear surface of the holder, while also using an O-ring to seal the other end of the cylindrical support member to a portion of the reaction chamber, electrode terminals are protected so as not to be exposed to the reactive gas.
In conventional semiconductor or liquid crystal manufacturing apparatus, a method is employed in which an O-ring is used for hermetic sealing between the cylindrical support member housing the electrode terminals and the reaction chamber in order to protect the electrode terminals on the rear surface of the holder from the corrosive gas. The airtightness required is thought to be at least the equivalent of a He leak of less than 10−8 Pa·m3/s with respect to a He leak. However, whereas O-ring sealing is reliable for such a convenient and inexpensive method, because the O-ring consists of rubber, the upper temperature limit is at most 200° C. even when a comparatively heat-resistant material is used.
Film formation, etching, heat treatment, and similar processes in the manufacturing of semiconductor or liquid crystal often involve the driving of reactions at temperatures of 200° C. and higher; in particular, in CVD and plasma CVD processes employed in film formation, high temperatures between 500 and 800° C. are often used. Consequently the vicinity of the O-ring must be forcibly cooled to maintain a temperature of less than 200° C., in order that the O-ring is not degraded due to heat conveyed through the cylindrical support member. As a result, 50% or more of the supplied heat is wasted without being used for the wafer heating for which it was intended.
Further, when a cylindrical support member is formed from ceramic material, if a large thermal gradient appears in the cylindrical support member the brittle ceramic material may crack, and so it has been necessary to use a long cylindrical support member of length approximately 300 mm, in order to mitigate the temperature gradient. The reaction chamber into which this long cylindrical support member must be placed cannot be reduced in size, and so an unnecessarily large structure becomes unavoidable.
Further, the hermetic sealing of cylindrical support member prevents the intrusion of halogen or other corrosive gas from within the reaction chamber; but often the cylindrical support member is used in an atmospheric environment. In such cases the electrode terminal vicinity is exposed to an oxidizing air atmosphere at a temperature of 500 to 800° C., so that the electrode terminals of W or Mo, with poor oxidation resistance, must be protected by applying an oxidation-resistant seal. However, it is not an easy task to apply such a seal deep within the long cylindrical support member, and so production yields are poor.